The present invention relates to a radar detectable balloon. The balloon includes an envelope which, when inflated, includes radar reflective planar faces arranged to efficiently reflect radar. When the envelope is not inflated, it assumes a compact, collapsed configuration. The balloon device may be incorporated in a kit, including an inflator for the balloon, for use in rescue operations or the marking of selected locations.
U.S. Pat. No. 2,619,303 discloses a signal buoy balloon which when inflated assumes a spherical shape. The balloon itself is impregnated with metallic material so that the balloon may be detected by electrical search means such as conventional radar apparatus. However, the curved surfaces of spherical or ovoid shaped balloons do not efficiently reflect radar.
U.S. Pat. No. 3,181,158 discloses a water-borne distress unit that includes a balloon whose envelope when inflated assumes a hexahedral configuration and acts as a radar reflector by virtue of a metallized surface. The hexahedral configuration of the balloon is also relatively inefficient at reflecting radar signals.
U.S. Pat. Nos. 2,888,675, 3,299,291, 4,901,081 and 5,457,472 disclose various multi-faceted radar reflectors. However, the reflectors are enclosed within a distinct envelope which is pervious to radar. Such constructions are complicated, requiring the reflectors to be attached to the internal surfaces of the balloon envelope.
According to a first embodiment, this invention provides a radar detectable balloon device comprising an inflatable envelope, wherein when inflated the envelope includes at least six radar reflective planar faces arranged in such a way that the largest angle formed by every line of sight and a normal to at least one planar face is less than 45xc2x0.
According to another embodiment, the balloon device comprises an inflatable envelope, wherein when inflated the envelope comprises at least eight radar reflective planar faces.
The envelope may include two polyhedral chambers, for example, chambers having pyramidal configurations. Such chambers are preferably joined at or near an apex of side facets of the pyramidal chambers. The chambers may be fluidly connected, and proximate pairs of edges of side facets of the pyramidal chambers may be joined by radar reflective webbing.
Additionally, this invention provides a kit comprising the balloon device, along with an inflator for selectively inflating the envelope with lighter than air fluid. The kit may further include a tether connected to the balloon device, and a storage pouch for storing the balloon device in a deflated condition, the inflator, and the tether. The storage pouch preferably has a weight that is greater than the buoyancy force of balloon device when inflated with the lighter than air fluid, to thereby serve as an anchor for the inflated device. The pouch may be sized to be easily retained within the pocket of a jacket. Alternatively, it may be incorporated into a flotation device or life raft.